1. Field of the Invention
The present invention relates to a tape travel controlling apparatus for use with, for example, a helical scan type data recorder for recording digital data as helical tracks on a magnetic tape with a rotating head.
2. Description of the Prior Art
As an external data storage unit for use with a computer or the like, a magnetic tape unit is known. As an example of the magnetic tape unit, a helical scan type unit that records digital data on a cassette tape with a rotating head is known. Whenever the magnetic tape unit receives a position traveling request from a host computer, the magnetic tape unit should travel the tape so as to detect the top position of data to be written or read. Hereinafter, the operation for detecting the top position of desired data (or file) is referred to as a top position detecting operation.
Next, with reference to FIGS. 22A, 22B, 22C, and 22D, the top position detecting operation used in a conventional data recorder will be described. FIGS. 22A, 22B, 22C, and 22D show an example of a tape on which two files are recorded. At the last end position of each file, a TM (Tape Mark) that represents a delimiter of a file is recorded. The last TM of the second file is followed by an EOD (end of data) that represents the last end position of data.
FIG. 22A shows data positions on a tape in the state just after the tape has been just loaded into the data recorder. Thus, the position of the access pointer (that is the head position) is unknown.
When the host computer sends a rewind request to the data recorder, it performs a rewind operation. In other words, as shown in FIG. 22B, the data recorder returns the access pointer to the tape top position as a first access operation to the tape. After the data recorder has rewound the tape, the data recorder stops traveling the tape and sends an acknowledge signal to the host computer.
Thereafter, the data recorder receives a top position detecting request from the host computer. For example, the data recorder receives from the host computer a request for skipping one TM (namely, the data recorder receives from the host computer a top position detecting request for detecting the second file). Thus, the data recorder searches a TM on the tape. When the data recorder detects a TM on the tape, it stops traveling the tape and sends an acknowledge signal to the host computer. In such a manner, the data recorder accesses the tape twice. When the data recorder receives a read request from the host computer, the data recorder starts reading data from the position of the access pointer.
Thus, when the top position detecting operation is performed for the read/write operations, a rewind operation for returning the tape to the tape top position and a forward operation for traveling the tape to a desired position are required. Consequently, since the tape is often traveled and a long access time is required, the tape tends to be damaged.
Thus, an object of the present invention is to provide a data recorder that reduces the number of tape traveling operations, that quickly accesses desired data on a tape, and that satisfactorily prevents the tape from being damaged.
Another object of the present invention is to provide a data recorder that prevents a time-out error from taking place in the case that a tape is traveled for a long distance between the present position and a target position and thereby it takes a long time.
The present invention is a tape travel controlling apparatus for use with a data recorder for recording and/or reproducing digital data on and/or from a tape-shaped recording medium, comprising a controlling means for providing a target position signal for representing a target position to which the tape-shaped recording medium is traveled, a first command signal for representing a position traveling request for the tape-shaped recording medium, and a second command signal for representing a write request or a read request for the tape-shaped recording medium, a storing means for detecting information of the target position of the tape-shaped recording medium from the traveling position signal and for storing the information when the first command signal and the target position signal are provided, a detecting means for detecting the present position of the tape-shaped recording medium and for outputting a present position signal for representing the present position of the tape, a comparing means for comparing the difference between the present position and the target position stored in the storing means with a predetermined value and for outputting a control signal for traveling the tape-shaped recording medium to a particular position between the present position and the target position when the difference is larger than the predetermined value, and a driving means for traveling the tape-shaped recording medium to the particular position between the present position and the target position when the first command and the control signal are provided and for traveling the tape-shaped recording medium from the particular position to the target position.
A target position mark is written on a tape position management table in a memory. Only when a write request or a read request is received, the tape is actually traveled. Thus, the traveling of the tape can be minimized. Consequently, the top position detecting operation can be quickly performed and the tape damage can be reduced. When the present access position is far from a target position, the tape is traveled beforehand so that the access position approaches the target position. Thus, a time-out error can be prevented.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of best mode embodiments thereof, as illustrated in the accompanying drawings.